the Active Directory service is central component in any windows server starting from windows server 2000. modern operating systems require mechanisms for managing the identities and relationships of the distributed resources that make up network environments. A directory service provides a place to store information about network-based entities, such as applications, files, printers, and people. It provides a consistent way to name, describe, locate, access, manage, and secure information about these individual resources. It is the central authority that manages the identities and brokers the relationships between these distributed resources, enabling them to work together Active Directory lets organizations efficiently share and manage information about network resources and users. In addition, Active Directory acts as the central authority for network security, letting the operating system readily verify a user’s identity and control his or her access to network resources. Equally important, Active Directory acts as an integration point for bringing systems together and consolidating management tasks. Active Directory is the first enterprise-class directory service that is scalable, built from the ground up using Internet-standard technologies, and fully integrated with the operating system. In addition to providing comprehensive directory services to Windows applications, Active Directory is designed to be a consolidation point for isolating, migrating, centrally managing, and reducing the number of directories that companies have. This makes Active Directory the ideal long-term foundation for corporate information-sharing and common management of network resources, including applications, network operating systems, and directory-enabled devices.

From Technical Point of view:

Active Directory lets organizations store information in a hierarchical, object-oriented fashion, and provides multi-master replication to support distributed network environments.

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